Portland cement will set and harden under water. Which of the following best describes this property?

• A. True
• B. False
• C. Only at high temperatures
• D. Only with silica fume

Answer: (A)

Portland cement is a hydraulic cement, meaning it hydrates and hardens in the presence of water. When water mixes with cement, the reactive compounds—primarily tricalcium silicate and dicalcium silicate—react to form calcium silicate hydrates (C-S-H) and calcium hydroxide. This chemical reaction creates a solid, interconnected matrix that gains strength even when submerged, so the paste will set and continue to harden underwater. The other options don’t fit because setting underwater does not require high temperatures, and it does not depend on silica fume; cement will hydrate underwater with or without silica fume.